The invention relates to integrated optical devices controllable fully by light comprising a protein as a material of non-linear optical property, and to complex integrated optical modules comprising the optical devices of the invention. The invention further relates to methods for carrying out logical operations and methods for the preparation of the ad-layer of the optical devices.
The optical device of the invention can be used in particular in the field of integrated optics, e.g. as a logical element, as an optical switch or as a sensor.
In the field of data processing or sensor technology optical systems (as opposed to the presently used type where the working basis is electrical) are generally believed to constitute the next generation with the promise of vastly improved performance in practically every aspect. The development of fundamental scientific knowledge and the required technology in the necessary fields forecasts the advent of revolutionary new devices either with direct applications or as building blocks of more complex systems.
At present, however, the level of the development of purely optical data processing devices is in its infancy; consequently, the development of highly complex systems seems not to be a task for the immediate future. Rather, the state of the art suggests a need for the testing of basic ideas, and finding the possibilities of basic classes of approaches.
Since the start of integrated electronics the expansion of development has been described by “Moore's law”: the density (performance) of integrated electronic circuits doubles about every 1.8 years. While this “law” has remained proven valid for a remarkable period of 30 years, there is a general perception that the evolutionary development has reached a limit. Molecular electronics combined with optical data processing is regarded as being among the most promising emerging alternative technologies.
Key solutions are expected to emerge on a new field of optics, called integrated optics. New type of logical circuits may be created from integrated optical devices (IOD) integrated on a small substrate as various optomodules. The fundamental unit of an integrated optical device is an optical waveguide. Via a prism or a grating coupler, light may be confined to a high refractive index, thin waveguide layer, the totally reflecting walls of which result in a phenomenon analogous to the quantum mechanical particle in a box. Here the walls are of finite height and thickness, hence the field is a standing wave within the box and evanescent beyond the walls, dying away exponentially. Only certain discrete modes (transversal electronic, TE and transversal magnetic, TM modes) can exist within the box that can be characterized by the Maxwell equations.
If the waveguide is coated with an applied medium (ad-medium) or preferably a thin film (or ad-layer) comprising a nonlinear optical (NLO) material, which (interacting with the evanescent part of the light beam) are capable of manipulating the light by changing one or more of their optical properties under the influence of an applied voltage or another light beam, the so obtained device can be utilized in integrated optics.
Intensive research is going on to seek the most suitable NLO materials that could meet the demanding requirements of applications, in particular high sensitivity accompanied with high stability [Service, R. F., (1995)].
The basis of operation is that the refractive index of the ad-layer changes according to an external perturbation.
Since the theory and measuring techniques for integrated optics are well-developed [see e.g. K. Lizuka: Engineering Optics (Springer-Verlag, Berlin, Heidelberg, 1987)], the main limitations are of a technical nature, namely to find the proper NLO materials for the particular applications envisaged.
In the field of integrated optics most frequently liquid crystals are used as NLO materials. Nevertheless, usually their electrooptical effect is utilized, that is light-control is carried out indirectly via photoelectronic converters (e.g. photodiodes) [see K. Lizuka: Engineering Optics (1987), above]. Up to the present, the art does not teach nor suggest fully light driven, integrated optical devices comprising protein as photochromic material. In particular, the art does not disclose the use of such photochromic proteins in ad-medium of integrated optical devices. Further, according to the art no disclosure of the manipulation of the propagating light in the waveguide by light controlled change of the refractive index of such ad-layers can be found. There exists a need, however, for such devices in the pertinent field of art.
The invention is based on the finding that a simple and reliable integrated optical device can be provided if an appropriate protein is used as an NLO material and an appropriate setup (arrangement), disclosed herein, is used.
An optical switch for optical fibres and working on a basis different from integrated optics is disclosed by Kobayashi Y. and Matsuda Y in EPA 0,433,901, wherein the use of a fulgide combined with a macromolecular polymer in optical fibres [mainly used in the field of telecommunication and having a significantly larger thickness than integrated optical (IO) waveguides] is described. Furthermore, in their device, though it works on the basis of changing the refractive index of the medium coating the fibre, a modulation event can take place only if the refractive index of the whole medium is nearly the same as that of the light coupling region. In EPA 0,532,014 [Hosoya, T. (1993)] an improved version of said switch is disclosed, in which the photosensitive material is placed between two waveguides. Again, precise setting of the refractive index of the medium carrying the photosensitive material is crucial.
Up until now the relating field of art has remained silent regarding the combination of photosensitive proteins and integrated optics.
During the past 10 years, several laboratories in the USA, Europe and Japan have worked on the development of parallel-processing devices, three-dimensional data-storage hardware and neural networks based on photosensitive proteins, in particular on bacteriorhodopsin (bR) [see, e.g., Parthenopoulos, D. A. and Rentzepis, P. M. (1989), Oesterhelt, D., Brauchle, C. and Hampp, N. (1991), Birge, R. R. (1992), Birge, R. R. (1994)]. The suggested applications so far have concentrated on optical data storage [Lewis A. et al, (1995), U.S. Pat. No. 5,470,690], sensor technology [Sakai T et al (1989) U.S. Pat. No. 4,804,834] and holography [Trantolo, D. (2000), WO 00/30084].
An optical switch utilizing the proton pump property of bR is disclosed in JP2310538 [Watanabe T., (1990)]. In U.S. Pat. No. 5,757,525 [Devulapalli V. G. L. N. R. et al., (1998)] an all optical device is described, in which three input radiation fields spatially overlapping on a bR sample are applied in a special geometry. Irradiation of the sample by a modulating radiation field results in a change in the bR state and consequently in the signal. No waveguides, so important in integrated optics, are used in either of the above solutions. In U.S. Pat. No. 5,618,64 [Hiroyuki T. and Norio S. (1997)] well defined partially permeable mirrors are used to control light transmission on the bR layer placed between the mirrors.
Neither of the above applications aimed and is not appears to be applicable in the field of integrated optics.